Setpoint generator for control of an electrically controlled brake system

ABSTRACT

The setpoint generator according to the invention utilizes the information &#34;pedal travel s&#34; in combination with the information &#34;pedal force p&#34; by weighting them in input circuits 4,5 and summing up the corresponding partial setpoints p&#39; s  and p&#39; p  to form a setpoint p&#39; Hz . Here, a countercurrent weighting takes place: If a small force acts on the pedal, the pedal travel is dominant; as the pedal force is growing, the latter is weighted more heavily. In this way, a smooth brake behavior is attained, whereby the comfort is enhanced and the wear of the employed components is reduced.

BACKGROUND OF THE INVENTION

The present invention relates to a setpoint generator, in particular fora brake pedal in an automotive vehicle for the control of anelectrically controlled brake system, with at least two parallelyconnected sensors working in accordance with different principles, withsubsequently connected electronic input circuits.

Such a setpoint generator, in particular for a brake pedal in anautomotive vehicle, is known from published German patent application 3504 096. It is for the control of an electric brake system and contains aparallel connection of a travel sensor and a force sensor, the forcesensor supplying the reference variable. To the sensors, there aresubsequently connected electronic main circuits which verify the sensorsignals according to diverse criteria with respect to plausibility, andwhich, in case of an error, trigger a warning light. In order to providea maximum extent of safety and accuracy, the sensors of the knownsetpoint generator proceed on different principles, and only in case ofa stated malfunction of the force sensor, the reference variable issupplied by the travel sensor.

It is to be regarded as a disadvantage of the known setpoint generatorthat, in particular for exceptionally small signals, the random noise isin the order of magnitude of the signals and thereby distorts them.Hence, there is provided a filtration of the signals which, however,results in a bad temporal behavior, i.e. a slow reaction. This conveysan inert vehicle behavior to the driver which is undesirable. If,however, no filtration is carried out, an uneven braking behavior willoccur, which, as well, is felt to be disturbing.

An object of the invention therefore is to prevent the disadvantages ofthe known setpoint generator and thus to enhance the comfort.

SUMMARY OF THE INVENTION

This object is achieved in that, for the generation of an electricsetpoint, the output signals of the sensors are weighted in theelectronic input circuits, and respective partial setpoints are summedup. Preferably, the output signals of the sensors are weighted in a waythat, in the ranges where a bad signal/noise ratio is found, thecorresponding sensor signal has a lesser share than the one that is notdisturbed as heavily, so that in total a largely smooth setpoint ensues.Thus, over the entire range of operation, a lesser random noise isattained.

It is provided that the weighting occurs in dependence of the outputsignal of at least one of the sensors. Here, the weighting may bedependent on the sensor signal itself. The weighting factor thus forinstance is small when the signal itself is small and thus shows a badsignal/noise ratio. Provided that there is a characteristic range inwhich a known disturbance of the sensor signal appears, an accordinglysmall weighting factor can be provided in this range. Further on, it isprovided to make the weighting factor also dependent on the signal ofthe other sensor, for example if the signal of the one sensor issupposed to get a low weighting while the weighting factor of the othersensor signal is supposed to be large, or vice versa.

According to the invention, it is further on provided that the weightingoccurs also in dependence of other sensor signals available inautomotive vehicles. These can be signals of a temperature sensor, ahumidity sensor or another suitable sensor. The weighting of the sensorsignals hence can also be adapted to a temperature dependent orhumidity-dependently varying characteristic.

The weighting, accordingly, can correspond to a simple analyticalfunction. Preferably, however, at least one special weighting functionis used which, for instance, may be stored in the electronic inputcircuitry. This weighting function can be derived individually for eachvehicle type and optimally adapted to this vehicle type and the desiredbrake characteristic by way of experiments or as a result of simulatingcalculations or other suitable methods. The weighting function derivedthis way may then be stored in a vehicle-specific read-only memory or,as well, in an overwritable memory. It is provided to store only oneweighting function if, from this one, the one or more other weightingfunctions can be derived (e.g. are complementary). Several differentweighting functions have to be stored if they are independent from eachother, or if, for other reasons, it appears to make sense storing themseparately.

Depending on structure and requirements of the electronic brake system,it can be advantageous to derive a setpoint for the pressure of ahydraulic brake system or for the actuation travel of a brake pad bysummation of the partial setpoints or, alternatively a setpointproportional to the deceleration to be attained. In this way, thesetpoint generator can be adapted to the most diverse brake systems.

Generally, one of the variables for the setpoint will be decided on(pressure, travel, or the like) and processed by a controller whichemits an appropriate control variable. There is, however, anotheradvantageous possibility of having several different variables processedby respective controllers and only summing up the according controlvariables. In this way, the driving comfort can be further enhanced aswell as a redundancy in the control circuit can be achieved.

Especially coordinated characteristics are provided by travel sensor andpressure sensor. In a hydraulic brake system, a high volume intake(corresponds to a large pedal travel) occurs at the beginning of a brakeoperation at low pressure, while during the further course of the brakeoperation, even with a slight pedal travel, a large pressure changeoccurs. Thus, the travel sensor delivers a low-noise signal in the rangewhere the pressure sensor shows a bad signal/noise ratio, and viceversa. Since, also with an electric brake system, the driver should havethe brake feeling that he is familiar with from the hydraulic brakesystem, here, as well, the equivalent characteristics appear.

Further advantages of the invention arise from the following descriptionin the light of the pictures.

BRIEF DESCRIPTION OF THE DRAWINGS IN THE DRAWINGS,

FIG. 1 shows a diagram of the master cylinder pressure p_(Hz) (V) as afunction of the volume intake V of a hydraulic brake system;

FIG. 2 shows a schematic presentation of the weighting and superpositionof the sensor signals according to the invention;

FIG. 3 shows an example of particularly simple weighting functions; and

FIG. 4 shows a schematic example for the further processing of thedetermined nominal signal.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a diagram of the master cylinder pressure p_(Hz) (V) as afunction of the volume intake V of a hydraulic brake system is depicted.It can be seen that, already at a low pressure p_(Hz), a large volumeintake occurs, while during the further course of the brake operation asteep pressure increase accompanies even a slight volume intake V. Thevolume intake V here is proportional to the pedal travel s, while themaster brake pressure prevailing in the brake system is proportional tothe pedal force that is to be applied by the driver.

FIG. 2 shows, in a schematic presentation, the weighting andsuperposition of the sensor signals. At a pedal 1, a travel sensor 2 anda pressure sensor 3 are located. Here, the pressure p is proportional tothe pedal force F. The output signals s, p of the sensors 2, 3 areweighted in input circuits 4, 5 and result in partial setpoints p'_(s)and p'_(p), which are added up in a summer 6 to form a setpoint p'_(Hz).In the input circuit 4, the weighting function f_(s)→p' (s) is storedwhich weighs the travel signal in dependence of itself and converts itinto the partial setpoint p'_(s).

Alternatively, the derivation of the setpoint of the travel x'_(Hz) of abrake pad from the partial setpoints x'_(s) and x'_(p) is indicated inparentheses. For this purpose, in the input circuits 4 and 5, theaccording weighting functions f_(s)→x' (s) and f_(s)→p' (s) are storedrespectively.

Further on, it is indicated schematically that a temperature signal Tand/or a humidity signal h can be provided as input variables of theinput circuit 4. The according weighting function then is also dependenton the values T and h, respectively: f_(s)→p' ((s,T,h). Neither thisdependence is explicitely shown in FIG. 2, nor is the, naturally alsopossible, impact of the respective signals on the input circuit 5.

In FIG. 3, ramp functions are shown as an extremely simple example forthe weighting functions. In this example, the weighting functions arechosen complementary, i.e. their sum always equals "1". In this case, itis possible to store only one of the weighting functions and to derivethe others from this one. The usual case, however, is, as alreadymentioned in the introductory part of the description, to chose theweighting functions dependently on the vehicle type and, for instance,to store them as a charactaristic curve.

In FIG. 4, it is schematically illustrated how the determined setpointp'_(Hz) can further be processed. To this end, a controller 7 determinesa control variable, in this case the current I, with which the electricmotor 8 is loaded. The electric motor 8 shifts a plunger 9 which isguided in a cylinder 10. The thereby displaced volume V reaches thewheel brake 11 and thus shifts the brake pads. As actual values, theactual current value i_(ist) as well as the travel x_(ist) of theplunger 9 can be fed back to the controller 7. As a setpoint, instead ofp'_(Hz), also x'_(Hz) can be used. A combination in which the twosetpoints are respectively supplied to a controller 7 and a controller7', indicated in dashed lines, is an alternative shown as well. Therespective control variables are added up in the summer 6' and forwardedto the electric motor.

The setpoint generator according to the invention thus utilizes theinformation "pedal travel s" in combination with the information "pedalforce p" by weighting them in the input circuits 4,5 and summing up thecorresponding partial setpoints p'_(s) and p'_(p) to form a setpointp'_(Hz). Here, a countercurrent weighting takes place: If a small forceacts on the pedal, the pedal travel is dominant; as the pedal force isgrowing, the latter is weighted more heavily. In this way, a smoothbrake behavior is attained, whereby the comfort is enhanced and the wearof the employed components is reduced.

What is claimed is:
 1. A setpoint generator for a pedal in anelectrically controlled system, comprising:at least two parallelyconnected sensors working in accordance with different principles andgenerating different sensor output signals, electronic input circuits,coupled to said output signals, for generating an electric setpointsignal, wherein the output signals of the sensors are weighted in theelectronic input circuits, and are summed to form said electric setpointsignal, wherein the weighting takes place in dependence on at least oneof a temperature sensor signal or an humidity sensor signal, and whereinsaid weighting is effective for reducing the signal to noise ratio ofsaid electric setpoint signal.
 2. The setpoint generator according toclaim 1, wherein the weighting takes place according to at least oneweighting function which is stored in the electronic input circuits. 3.The setpoint generator according to claim 1, wherein the pedal is abrake pedal and each input circuit delivers a partial setpoint foradjusting the pressure in a hydraulic brake system.
 4. The setpointgenerator according to claim 1, wherein the pedal is a brake pedal andeach input circuit delivers a partial setpoint for adjusting a brake padtravel.
 5. The setpoint generator according to claim 1, wherein thepedal is a brake pedal and each input circuit delivers a partialsetpoint for adjusting vehicle deceleration.
 6. The setpoint generatoraccording to claim 1, wherein the setpoints for different variables aredetermined which are each processed by a respective controller.
 7. Asetpoint generator for a pedal in an electrically controlled system,with at least two parallely connected sensors working in accordance withdifferent principles and generating different output signals, withsubsequently connected electronic input circuits, wherein, for thegeneration of an electric setpoint, the output signals of the sensorsare weighted in the electronic input circuits, wherein the partialsetpoints are summed, and wherein the weighting of at least one outputsignal of one of said sensors takes place in dependence on the output ofat least one of the sensors, and wherein said weighting is effective forreducing the signal to noise ratio of said electric setpoint.